Incorporation Of Polyhedral Oligomeric Silsesquioxane Research Articles

Comparative study on the synergistic effect of POSS and graphene with melamine phosphate on the flame retardance of poly(butylene succinate)

Flame retardant poly(butylene succinate) (PBS) composites were prepared by melt blending PBS with melamine phosphate (MP), using graphene or polyhedral oligomeric silsesquioxanes (POSS) as synergists. The comparative study on the effect of POSS and graphene on the mechanical, thermal properties and flammability of flame retardant PBS was investigated. The addition of POSS or graphene further improved the LOI values of the flame retardant PBS, and V0 rating was obtained for the formulation containing 18 wt% MP and 2 wt% graphene. The incorporation of POSS and graphene reduced the crystallization of PBS, but improved the tensile strength. The presence of graphene exhibited superior thermal-oxidative resistance of the char layer compared to POSS, which effectively retarded the mass and heat transfer between the flame and the burning substrate, thus the heat release rate and total heat release of the flame retardant PBS composites containing graphene was significantly reduced during combustion.

Properties of POSS/HNBR Elastomer Nanocomposites

A series of composite materials containing polyhedral oligomeric silsesquioxanes (POSS) and hydrogenated butadiene-acrylonitrile rubber (HNBR) were prepared. The goal of the work was to evaluate the effect of the type and reactivity of functional groups in the POSS cage on properties of the resulting elastomeric nanocomposites. The paper presents some of the preliminary results obtained from the studies. The results indicate that incorporation of POSS into silica-filled HNBR elastomer network increases interfacial interactions of the systems and the POSS molecules can be successfully used as coagents of crosslinking towards the elastomer matrix and efficient additives improving the mechanical properties of elastomeric nanocomposites. Furthermore, evaluation of changes in mechanical properties, induced in a result of POSS/HNBR composites ageing, show that the inclusion of POSS in the HNBR network is directly influencing the stabilizing effect and improves the ageing resistance of elastomer composites.

Synthesis and characterization of polyhedral oligomeric silsesquioxane–siloxane-modified polyimide hybrid nanocomposites

Polyhedral oligomeric silsesquioxane (POSS)–siloxane-modified polyimide (PI) hybrid nanocomposites were prepared by the reaction of siloxane-modified polyamic acid (PAA) with octaaminophenylsilsesquioxane (OAPS). PAA was prepared by the reaction of 4,4-diaminodiphenylsulfone with pyromellitic dianhydride in N-methylpyrrolidone (NMP), followed by the reaction of PAA with bis(3-aminopropyl) polydimethylsiloxane to obtain siloxane-modified. The siloxane-modified PI was further blended with varying weight percentages of OAPS using NMP solution. The reactions occurred during the formation of hybrid nanocomposites were confirmed by Fourier transform infrared spectra. The siloxane-modified PI OAPS nanocomposites were characterized for their thermal properties using differential scanning calorimeter and by thermogravimetric analysis. Morphological studies of the nanocomposites indicate that the incorporation of siloxane moieties creates heterogeneous morphology. Data from thermal studies indicate that the incorporation of POSS appreciably enhanced the glass transition temperature, thermal stability, and char yield of hybrid nanocomposites compared to neat PI.

Synthesis and characterization of bisphenol-A ether diamine-based polyimide POSS nanocomposites for low K dielectric and flame-retardant applications

Polyhedral oligomeric silsesquioxane (POSS) – polyimide (PI) hybrid nanocomposites were prepared by a two-step approach, bisphenol-A ether diamine (BAED) and pyromelletic dianhydride (PMDA) in 1-methyl-2-pyrrolidone (NMP) were used to prepare polyamic acid (PAA) to which varying weight percentages of OAPS in NMP were added. During the second step, the polycondensation was effected by thermal imidization. The formation of hybrid nanocomposites was confirmed by using FTIR spectra. The thermal properties of POSS-PI nanocomposites were studied using differential scanning calorimetry and thermogravimetric analysis. The lowest dielectric constant 2.68 was achieved for 15 wt.% POSS-PI material when compared with the value of 3.34 for the neat PI. Data from thermal studies indicate that the incorporation of POSS into polyimide significantly enhanced the glass transition temperature ( Tg), thermal stability, char yield and flame-retardant properties of hybrid nanocomposites than that of neat PI. The excellent combination of both dielectric and thermal properties of the material developed in the present study will find application in microelectronics.

Microstructure and Crystallization Kinetics of Polyurethane Thermoplastics Containing Trisilanol Isobutyl POSS

The synthesis of thermoplastic polyurethanes (TPU) from the reaction of a NCO group‐containing prepolymer and 0, 1.14, 1.71, and 2.28 wt% of trisilanol isobutyl polyhedral oligomeric silsesquioxane (POSS) was carried out in an instrumented batch mixer. The samples were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X‐ray diffraction (XRD), and scanning electron microscopy (SEM). SEM analysis shows that the incorporation of POSS promoted strongly aggregation through physical interactions (formation of POSS‐rich domains). Modifications in the TPU microstructure and the reduction in the crystal size were observed in the XRD diffractograms. The incorporation of POSS equally altered the TPU crystallization, and samples bearing higher concentrations of POSS formed two distinct types of crystalline structures. The kinetics of crystallization showed that nucleation strongly depends on the balance between TPU crystal formation and POSS‐rich domains.

Thermal Degradation Characteristics and Kinetics of High Temperature Vulcanized (HTV) Silicone Rubber/POSS Hybrid

A high temperature vulcanized (HTV) silicone rubber/octavinyl polyhedral oligomeric silsesquioxane (POSS) hybrid was prepared. The micromorphology of the cured hybrid was investigated by scanning electron microscopy (SEM); the thermal degradation stability of this hybrid was studied by means of thermal gravimetric analyses (TGA); the degradation kinetics of this hybrid was also studied using Doyle method and Coats-Redfern method. Results showed that aggregation of self-cross-linked octavinyl POSS appeared in the HTV silicon rubber/POSS hybrid. The incorporation of POSS into silicon rubber networks enhanced the thermal degradation resistance of the matrix. Activation energy derived by the Coats-Redfern method (142.24 kJ/mol) showed a good agreement with the mean value derived by the Doyle method (146.51 kJ/mol); the thermal degradation reaction of the hybrid followed a three-dimensional diffusion law (D4).

Polyhedral Oligomeric Silsesquioxane (POSS) Suppresses Enzymatic Degradation of PCL-Based Polyurethanes

In this Article, we studied the enzymatic hydrolytic biodegradation behavior of a novel multiblock thermoplastic polyurethane (TPU) system, which incorporates polyhedral oligomeric silsesquioxane (POSS) into linear biodegradable thermoplastic polyurethanes containing poly(ε-caproactone) (PCL) and polyethylene glycol (PEG) blocks. The biodegradation behavior of POSS-PCL-PEG TPUs was characterized by proton nuclear magnetic resonance spectroscopy ((1)H NMR), differential scanning calorimetry (DSC), tensile tests, scanning electron microscopy (SEM), and wavelength dispersive X-ray spectrometry (WDS) after enduring 22-day accelerated enzymatic hydrolytic degradation tests. POSS incorporation significantly suppressed in vitro enzymatic hydrolytic degradation of PCL-PEG-based multiblock TPUs by a surface passivation mechanism. WDS observations revealed that the covalently bonded POSS moieties developed a near-continuous and robust POSS-layer after initial degradation, which prevented ester bonds of PCL from enzymatic attack, thereby inhibiting further degradation. These striking results provide a new strategy to fabricate the polyester-based biostable thermoplastic polyurethanes (TPUs) of potential use in long-term surgical implants.

Polyhedral oligomeric silsesquioxane–polyphenylsulfone nanocomposites: Investigation of the melt‐flow enhancement, thermal behavior, and mechanical properties

AbstractTwo structurally and chemically different polyhedral oligomeric silsesquioxane (POSS) molecules with different solubility parameters, dodecaphenyl POSS and trisilanolphenyl POSS, were melt‐blended with polyphenylsulfone (PPSU), and the effects on the material processing, rheology, and thermomechanical properties were investigated. Process monitoring and capillary rheometry revealed enhancements in the processing melt flow and a reduction in the nanocomposite viscosity with only a small addition of POSS. The magnitude and concentration dependence of rheological modification were shown to depend on POSS structure. Although small increases in the tensile modulus were observed, reductions in the tensile elongation properties were observed at high POSS loading levels. Analysis of the nanocomposite fracture behavior and surface morphology provided evidence for the surface phase segregation of both types of POSS, but the extent of segregation was related to the POSS structure. The degree of interfacial adhesion in the POSS/polymer composites and the resultant rheological behavior were related to the POSS composition and predicted solubility parameters. No measurable effect on the glass‐transition temperature or molecular weight of PPSU was observed, whereas small improvements in the thermal degradation behavior were obtained with the incorporation of POSS. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Studies on thermal and dielectric properties of ether linked cyclohexyl diamine (ELCD)-based polyimide POSS nanocomposites (POSS-PI)

Polyhedral oligomeric silsesquioxane (POSS)-polyimide (PI) hybrid nanocomposites were prepared from ether linked cyclohexyl diamine (ELCD)-modified polyamic acid with POSS derivative of octaaminophenylsilsesquioxane (OAPS). Polyamic acid (PAA) was prepared by reacting ELCD with pryomelletic dianhydride (PMDA) in 1-methyl-2-pyrrolidone (NMP) medium. The PAA reacted with varying weight percentages of OAPS and undergoes thermal imidization to form POSS-PI nanocomposites upon heating. The formation of hybrid nanocomposites was confirmed with Fourier transform infrared spectra. The thermal and dielectric properties of POSS-PI nanocomposites were characterized by using differential scanning calorimetry, thermogravimetric analysis and an impedance analyzer. Morphology of the nanocomposites was studied by using scanning electron microscopy. Data from thermal studies indicated that the incorporation of POSS in to PI substantially enhanced the glass transition temperature ( Tg), thermal stability and char yield of hybrid nanocomposites in comparison with those of neat PI. From the dielectric studies it was inferred that the increasing percentage concentration of OAPS into the PI network exhibits a decreasing trend in the values of dielectric constant when compared with those of neat PI.

Some recent developments of polyhedral oligomeric silsesquioxane (POSS)-based polymeric materials

Polyhedral Oligomeric Silsesquioxane (POSS) has attracted considerable interest in materials science due to its well-defined nano-scale organic–inorganic structure, which makes it an ideal building block for constructing nano-structured hybrid materials and nanocomposites. In this article, we highlight some recent developments in applications of POSS materials: 1) improving thermal and mechanical properties of polymers through incorporation of POSS into polymer matrices to form nanocomposites; 2) using POSS as a building block for design and synthesis of POSS-containing organic semiconductor materials to achieve high photo-luminescence/electron luminescence quantum efficiency in organic light emitting diodes and enhanced performance in electrochromatic devices; 3) exploiting POSS as a hydrophobic unit to develop amphiphilic polymers for drug/gene delivery and formation of hydrogels. A future direction for the development of POSS-containing materials is also proposed for applications in organic photovoltaic and other high-performance materials.

Cardiovascular application of polyhedral oligomeric silsesquioxane nanomaterials: a glimpse into prospective horizons

Revolutionary advances in nanotechnology propose novel materials with superior properties for biomedical application. One of the most promising nanomaterials for biomedical application is polyhedral oligomeric silsesquioxane (POSS), an amazing nanocage consisting of an inner inorganic framework of silicon and oxygen atoms and an outer shell of organic groups. The unique properties of this nanoparticle has led to the development of a wide range of nanostructured copolymers with significantly enhanced properties including improved mechanical, chemical, and physical characteristics. Since POSS nanomaterials are highly biocompatible, biomedical application of POSS nanostructures has been intensely explored. One of the most promising areas of application of POSS nanomaterials is the development of cardiovascular implants. The incorporation of POSS into biocompatible polymers has resulted in advanced nanocomposite materials with improved hemocompatibility, antithrombogenicity, enhanced mechanical and surface properties, calcification resistance, and reduced inflammatory response, which make these materials the material of choice for cardiovascular implants. These highly versatile POSS derivatives have opened new horizons to the field of cardiovascular implant. Currently, application of POSS containing polymers in the development of new generation cardiovascular implants including heart valve prostheses, bypass grafts, and coronary stents is under intensive investigation, with encouraging outcomes.

Hydrolytic degradation of POSS–PEG–lactide hybrid hydrogels

A polyhedral oligomeric silsesquioxane (POSS), functionalized with eight arms of poly(ethylene glycol) (PEG; MW 400) and then acrylated, was incorporated into a hydrogel network based on triblock copolymers of poly(lactide- b-ethylene glycol- b-lactide) diacrylates using a redox-initiated polymerization. The organic–inorganic hybrid hydrogels so prepared contained the inorganic crosslinker POSS from 1 to 28 wt.%. The degradation properties of the hydrogels in a pH 7.4 phosphate-buffered saline solution at 37 °C were studied using measurements of mass loss, cryogenic SEM, and ATR-FTIR spectroscopy. It was found that copolymerization of acrylated 1kPEG-lactide with increasing amounts of POSS created a more porous network which was more resistant to hydrolysis. The ATR-FTIR technique was used to monitor the progress of degradation with exposure time through the changes in the carbonyl and C–H deformation bands of the lactide and the Si–C stretching band of the POSS. Increasing POSS incorporation resulted in decreased rate of degradation due to its hydrophobic nature and inertness to hydrolysis. Conversely, an increase in lactide content increased the degradation rate due to the increased number of hydrolytically-sensitive ester groups in the network.

Glass transition and structural properties of glycidyloxypropyl-heptaphenyl polyhedral oligomeric silsesquioxane-epoxy nanocomposites

We have used molecular simulations to study the properties of nanocomposites formed by the chemical incorporation of polyhedral oligomeric silsesquioxane (POSS) particles in the cross-linked epoxy network. The particular POSS molecule chosen—glycidyloxypropyl-heptaphenyl POSS—can form only one bond with the cross-linker and thus was present as a dangling unit in the network. Four epoxy-POSS nanocomposites containing different fractions (up to 30 mass/%) of POSS particles were studied in this work. Well-relaxed atomistic model structures of the nanocomposites were created and then molecular dynamics simulations were used to characterize the density, glass transition temperature (Tg), and the coefficient of volume thermal expansion (CVTE) of the systems. In addition to the effect of nanoparticle loading, the effect of nanoparticle chemistry on the nanocomposite properties was also characterized by comparing these results with our previous results (Lin and Khare, Macromolecules 42:4319–4327, 2009) on neat cross-linked epoxy and a nanocomposite containing a POSS nanoparticle that formed eight bonds with the cross-linked network. Our results showed that incorporation of these monofunctional POSS particles into cross-linked epoxy does not cause a measurable change in its density, glass transition temperature, or the CVTE. Furthermore, simulation results were used to characterize the aggregation of POSS particles in the system. The nanofiller particles in systems containing 11, 20, and 30 mass/% POSS were found to form small clusters. The cluster-size distribution of nanoparticles was also characterized for these systems.

Characterization of PBT/POSS nanocomposites prepared by in situ polymerization of cyclic poly(butylene terephthalate) initiated by functionalized POSS

AbstractNovel poly(butylene terephthalate) (PBT)/polyhedral oligomeric silsesquioxane (POSS) nanocomposites were synthesized by ring‐opening polymerization of cyclic poly(butylene terephthalate) initiated by functionalized POSS with various feed ratios. The impact of POSS incorporation on melting and crystallization behaviors of PBT/POSS nanocomposites was investigated by means of X‐ray diffraction and differential scanning calorimetry. It was found that the novel organic–inorganic association result in the significant alterations in the melting and crystallization behavior of PBT. Thermal studies confirmed that the incorporation of POSS can enhance the thermal stability of the polymers, and the copolymer glass transition temperature increased with the increasing of POSS macromonomer content. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1853–1859, 2010

Biocompatibility of synthetic poly(ester urethane)/polyhedral oligomeric silsesquioxane matrices with embryonic stem cell proliferation and differentiation.

Incorporation of polyhedral oligomeric silsesquioxanes (POSS) into poly(ester urethanes) (PEU) as a building block results in a PEU/POSS hybrid polymer with increased mechanical strength and thermostability. An attractive feature of the new polymer is that it forms a porous matrix when cast in the form of a thin film, making it potentially useful in tissue engineering. In this study, we present detailed microscopic analysis of the PEU/POSS matrix and demonstrate its biocompatibility with cell culture. The PEU/POSS polymer forms a continuous porous matrix with open pores and interconnected grooves. From SEM image analysis, it is calculated that there are about 950 pores/mm(2) of the matrix area with pore diameter size in the range 1-15 µm. The area occupied by the pores represents approximately 7.6% of the matrix area. Using mouse embryonic stem cells (ESCs), we demonstrate that the PEU/POSS matrix provides excellent support for cell proliferation and differentiation. Under the cell culture condition optimized to maintain self-renewal, ESCs grown on a PEU/POSS matrix exhibit undifferentiated morphology, express pluripotency markers and have a similar growth rate to cells grown on gelatin. When induced for differentiation, ESCs underwent dramatic morphological change, characterized by the loss of clonogenecity and increased cell size, with well-expanded cytoskeleton networks. Differentiated cells are able to form a continuous monolayer that is closely embedded in the matrix. The excellent compatibility between the PEU/POSS matrix and ESC proliferation/differentiation demonstrates the potential of using PEU/POSS polymers in future ESC-based tissue engineering.

Aminoethylaminopropylisobutyl POSS—Polyimide nanocomposite membranes and their gas transport properties

Abstract A series of polyimide-POSS (PI-POSS) nanocomposite membranes were prepared using aminoethylaminopropylisobutyl group functionalized polyhedral oligomeric silsesquioxanes (POSS) as nanofiller. The membranes were characterized by DSC, TGA, AFM, FESEM, XRD, etc. The effects of incorporation of POSS into the four structurally different fluorinated polyimide membranes on their gas transport properties with four gases (CH4, N2, O2 and CO2) were investigated at 35 °C and at an applied pressure of 3.5 atm. All the nanocomposite membranes showed comparable glass transition temperature values but a little lower thermo-oxidative stability compared to their corresponding untreated polyimide membranes. The Young's modulus and maximum stress values of the polyimide-POSS membrane were slightly higher than those of the virgin polyimide membranes; however the elongation at break values were lower. POSS nanoparticles were well distributed as observed from FESEM image and AFM study exhibited no significant increase of the roughness of the hybrid membranes. The order of permeability of these gases were found as CO2 > O2 > N2 > CH4. The permeability of all the gases through the composite membranes increased significantly with comparable selectivity for different gas pairs, e.g., CO2/CH4 and O2/N2.

Controllable Preparation and Optical Limiting Properties of POSS-Based Functional Hybrid Nanocomposites with Different Molecular Architectures

A series of soluble polyhedral oligomeric silsesquioxane (POSS) based inorganic−organic hybrid nonlinear optical materials with different architectures, such as dumbbell-type, bead-type and network-type structure, were prepared based on the hydrosilylation addition reaction of multifunctional octahydridosilsesquioxane (T8H) with different azobenzene chromophore monomers. These resultant hybrid composites are soluble in common organic solvents such as tetrahydrofuran, toluene, and chloroform, and exhibit good film-forming ability. Their structures and properties were characterized and evaluated with IR, 1H NMR, 29Si NMR, TGA, DSC, optical limiting measurement and Z-scan technique, respectively. The results show that the structure of these resultant hybrids can be effectively tuned by simply varying the feed ratio and molecular structure of organic chromophore monomers. The incorporation of inorganic POSS into organic azobenzene chromophore has endowed the hybrids with well optical limiting properties and high thermal stability. Simultaneously, the relationship between molecular structure and properties of these hybrids were investigated in detail.

The effect of incorporation of POSS units on polymer blend compatibility

AbstractIn this work, the compatibility of poly(methyl methacrylate) (PMMA) and polystyrene (PS) polymers with their polyhedral oligomeric silsesquioxane (POSS) copolymers combined by solution blending is investigated, to determine the effect of incorporation of the POSS unit on polymer compatibility. The morphology of these tethered POSS copolymer/polymer blends was studied by electron microscopy, thermal analysis, and density. Although the basic PS/PMMA blend was clearly immiscible, it was also found that the incorporation of POSS into the PS chain led to incompatibility when the POSScoPS copolymer was blended with PS homopolymer. However, conversely, in the case where the POSS moiety was included as part of a copolymer with PMMA, the copolymer was miscible with the PMMA homopolymer. The presence of isobutyl units on the corners of POSS cage is clearly sufficient to encourage miscibility with PMMA. Interestingly, blends of the two different POSS copolymers led to an immiscible structure, despite having the common POSS units, the interactions between the POSS moieties clearly not being sufficient to drive compatibility. The POSS copolymers have also been used as interfacial agents in immiscible PS and PMMA blend, and it has been found that the appearance of the interface bonding is improved, although the phase morphology is only slightly changed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

POSS‐nylon 6 nanocomposites: Influence of POSS structure on surface and bulk properties

AbstractHybrid organic/inorganic nanocomposites based on polyhedral oligomeric silsesquioxane (POSS) nanostructured chemicals and nylon 6 were prepared via melt mixing. Two structurally and chemically different POSS molecules, a closed cage, nonpolar octaisobutyl POSS (Oib‐POSS) and an open cage, polar trisilanolphenyl POSS (Tsp‐POSS) with differing predicted solubility parameters were evaluated in the nylon matrix. Surface analysis, including quasi‐static and dynamic nanoindentation and nanotribological techniques, revealed exceptional improvements in modulus and hardness along with significant reductions in friction. Additionally, surface wetting characteristics of the nylon were reversed, with POSS incorporation yielding low surface energy, highly hydrophobic surfaces. AFM, TEM/EDAX, spectroscopic techniques and thermomechanical analysis were used to evaluate nanoscale dispersion and bulk properties of the composites. Both POSS molecules exhibit preferential surface segregation behavior in the nylon matrix. Tsp‐POSS, with its higher predicted solubility in nylon, exhibited enhanced dispersion and tribomechanical properties at both nano and bulk scale. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1088–1102, 2009

Preparation and characterization of styrene/styryl–polyhedral oligomeric silsesquioxane hybrid copolymers

AbstractBACKGROUND: Organic–inorganic nanocomposites were prepared by copolymerization of various monomers and polyhedral oligomeric silsesquioxane (POSS) derivatives. Preliminary results showed that styrene/styryl–POSS copolymers could be obtained using CpTiCl3 catalyst. In the work reported here, the copolymerization of styrene and styryl‐substituted POSS was studied in detail for a more effective catalyst, Cp*TiCl3.RESULTS: The glass transition temperature (Tg) of the copolymers prepared increased with increasing POSS content. The degradation temperature (Td) of the copolymers was 60 °C higher than that of syndiotactic polystyrene under nitrogen. Although the thermal properties were improved by incorporation of POSS, the catalytic activity decreased with POSS content. The racemic triad and syndiotactic index of the copolymers decreased with increasing POSS content. Gel permeation chromatograms of the copolymers exhibited multimodal distribution due to the presence of multi‐active centres, which were formed by interaction of Ti with the POSS siloxane linkage.CONCLUSION: With the incorporation of POSS, the thermal properties of polystyrene were improved. The styrene/styryl–POSS copolymers are formed through the various active sites arising from the interactions of Ti with POSS. Copyright © 2008 Society of Chemical Industry